This invention relates to a process for preparing sulfur-containing compositions useful as additives for lubricant formulations.
Methods for the preparation of sulfur-containing additives for lubricants are, among others, described in U.S. Pat. No. 2,855,366, wherein an organic acid and/or ester is treated with sulfur, sulfur chloride, hydrogen sulfide, phosphorus pentasulfide and/or phosphorus sesquisulfide, at elevated temperatures. In said patent it is stated that, when one begins with natural oils and fats, sulfurizing will in many cases lead to products with a viscosity that is frequently much too high for the mentioned purpose, and to a solubility in mineral oils which is too limited. The disclosure of the patent thus suggests that one perform the sulfurization of the mentioned naturally occurring esters in the presence of a fatty acid, oleic acid.
The present invention provides an improved process for the preparation of sulfur-containing compositions useful as additives to lubricant compositions with even better viscosity behavior and greatly increased solubility in mineral oil fractions.